Re: The Bomb

[Aleksander Mierzwa <alex@matrix.pl>]

At 13:29 99-03-11 -0500, Mike Guidotti wrote:

>Ok, so all this talk about recharging bombs made me take notice of my own.
I get exactly >0, as in zero pumps! I assume that it is not working=) My
big question, is this a >problem??

Yes :-)

>The car seems to run great and I love the brake pedal feel. I do not leak
any pentosin at all.

It has nothing to do with pentosin leaks.

>Is this something that only becomes an issue if the car stalls so that you
can easily >stop it? Chances are I have been driving like this for the past
80K miles including lots >of track events. I use Pagid rs4 pads and SS
lines, it stops great. If I replace it will >I loose my nice firm pedal feel??

As Phil has nicely put it, "try to stop like this was _your_ child on the
road".
The most deceptive thing about a dead bomb is that the car seems to drive
OK. You can't see any problem until you compare it to a car which has a
working one. A dead bomb has no effect on pedal feel nor efficiency of
brakes unless one of two things happens:
1) ABS engages - all cars with vacuum assist have a separate electric pump
and pressure reservoir for activating ABS. On our Audis the pressure for
the ABS system is taken from - guess where - the bomb. So if the bomb is
bad, the ABS can still decrease the pressure in the brake system, but it
might not have the means to restore it...
2) You have to brake _really_ hard. The pump simply can't provide enough
fluid at required pressure when brake pedal is pressed to the floor
rapidly. Because those cars have excellent brakes, you still might think
that it brakes as it should... I believe a 5KT(Q) with G60 pistos will
outbrake many modern cars even with dead bomb, but with a working one it
stops much better, take my word for it. I was driving with a dead bomb for
2 years and too was thinking "what's the deal, it brakes OK" until the
flashing brake light and good advice from the list tempted me to replace
it. The first time I pressed the brakes to the floor after putting brand
new bomb in I knew it was money well spent.

Take note that the "bomb test" is best performed right after shutting the
engine off. The reason for this is that you might have a good bomb, but
slightly leaking servo. In this case the car will brake pretty much as it
should, but the bomb will start to discharge right after stopping the engine.

Aleksander Mierzwa
Warsaw, Poland
mailto:alex@matrix.pl
87 Audi 5000CS turbo (mine)
88 Renault Medallion wagon (mom's)
91 mountain bike (just in case both cars break at the same time :-)